It's not "too much vacuum" you either have an air leak or a lot of blowby. Let me explain, when you pull a vacuum on an engine, the oil can't go into the suction side of the pump unless something (air/blowby) can act on it and move it into the pump. I had this happen a bunch of times on the dyno, I take an electric vacuum pump and hook it up with the engine not running, and you can hear the leaks. FYI BBM leak a bunch at the front and rear seals, we use either a rear seal from "fastfish" or from tritec and have gotten good results.
